A South Philadelphia teen allegedly shot and killed his pregnant girlfriend early this morning because he did not want her to have his child, police said.

Police were called to the 2300 block of South Mildred Street at 2:40 a.m., where the body of Tiffany Gillespie, 24, laid in the basement. Her mother had discovered her after hearing a gunshot from the floor above. Gillespie, whose two young children were also at home at the time, had been shot in the head.

"Immediately, investigators focused on her boyfriend, Aaron Fitzpatrick, with whom she had a tumultuous relationship over the last couple months," Capt. James Clark of the Homicide Unit said this afternoon. "They had been arguing over the last 24 hour period. He was upset at the fact that she was pregnant with his baby." Investigators believe that to be the motive for the killing.

Police had been called out to the property several times in the past for domestic disputes, Clark said. Authorities arrested Fitzpatrick, 19, around noon and expect him to be charged with homicide. "Things fell into place real quickly," Clark said.

Officials will determine whether Fitzpatrick will be charged with a double homicide after the medical examiner's results reveal how long Gillespie had been pregnant.